This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The glycan determinant CD15 (also known as Lewis x, or Lex) is a distinguishing marker for human myeloid cells and mediates neutrophil adhesion to dendritic cells. Despite broad interest in this structure, the mechanisms underlying CD15 expression remain relatively uncharacterized. Accordingly, the Sackstein laboratory has investigated the molecular basis of increasing CD15 expression associated with human myeloid cell differentiation. Flow cytometric analysis of differentiating cells together with biochemical studies using inhibitors of glycan synthesis and of sialidases showed that increased CD15 expression is not due to de novo biosynthesis of CD15, but results predominantly from induction of a(2-3)-sialidase activity, which yields CD15 from cell-surface sialyl-CD15 (also known as sialyl-Lewis x, sLex or CD15s). This differentiation-associated conversion of surface CD15s to CD15 occurs mainly on glycoproteins. Until now, modulation of post-translational glycan modifications has been attributed solely to dynamic variations in glycosyltransferase expression. The results unveiled a new paradigm by demonstrating a critical role for post-Golgi membrane glycosidase activity in the 'biosynthesis'of a key glycan determinant. The Resource provided glycan profiles to respond to a reviewers'request during evaluation of the manuscript which reported these results. The Resource is also providing access to 2D-gel and LC/MS/MS equipment and training for postdoctoral fellow Christina Silvescu from the Sackstein laboratory who has previous experience in mass spectrometry.